This invention relates to an apparatus and a method for warming a variable-pitch propeller mechanism. More particularly, this invention relates to an apparatus and method for providing a flow of warm or hot air through an opening in the xe2x80x9cspinnerxe2x80x9d, or cover, of a variable pitch propeller mechanism.
Turbine-driven aircraft propellers may be equipped with a variable pitch mechanism. The purpose of this variable pitch mechanism is to permit the operator of the aircraft to xe2x80x9cfeatherxe2x80x9d the propeller or propellers, in order to effect a change in the amount of thrust provided to the aircraft by the propeller(s). This is valued because a change in propeller pitch can be performed more rapidly than a change in propeller rotational (angular) velocity, thereby giving the operator of the aircraft a responsive means for changing the amount of thrust applied to the aircraft.
An aircraft that is powered by a turbine engine or engines, having variable pitch propeller mechanism(s) and variable pitch propeller(s) is commonly referred to as a turbo-prop aircraft to distinguish it from a turbine driven aircraft without a propeller. Further, the combination of a turbine engine, transmission, variable pitch propeller and variable pitch propeller mechanism may itself be referred to as a turbo-prop, or as turbo-prop machinery.
Variable pitch mechanisms are produced in varying forms and configurations. In one family of configurations, hydraulic fluid, under pressure, is used to vary the pitch of the propeller blades. In mechanisms that use hydraulic actuation principles, seals are provided at numerous points within the variable pitch propeller mechanism to keep the oil contained within the hydraulic circuit, and thereby to prevent undesirable leakage of hydraulic fluid.
In order to insure reliable function, it is customary and necessary that routine inspection and troubleshooting be performed on various aspects of turbo-prop machinery. In some cases, for example to check whether the proper amount of fluid is in the hydraulic circuit, these procedures involve manually changing the pitch of the propeller. That is, in order to evaluate certain aspects of the condition of the variable pitch mechanism, the pitch of the blades is changed while the turbine engine is stationary, by grabbing one (or more) blade(s) of the propeller and twisting it, or by other means such as providing an external supply of hydraulic pressure to actuate a change in pitch. This manual manipulation must be done with the turbine engine off, and is usually done after the engine has been off for a significant period of time, e.g. overnight or a period of at least several hours.
In certain environments, and particularly in cold environments, the elastomeric material comprising the hydraulic seals becomes less compliant, i.e. the elastomer becomes rigid and takes a set. When the elastomeric material of the seal is in this non-compliant condition, the manual manipulation (i.e. moving by hand or other means while the turbine engine is stationary) or other movement of the variable pitch aspect of the propeller can result in damage to the seals. Seal replacement is time consuming and costly, and has an adverse impact on the ability to operate aircraft on schedule.
In order to avoid damaging the cold seals, it is necessary that the variable pitch propeller mechanism, including the seals, attain a warmer temperature before the pitch of the propeller blades is manually changed. The only practice for causing the increase in component temperature, before the introduction of the present invention, has been to tow the aircraft to a heated hangar structure in order to effect the necessary warming. After the aircraft and variable pitch propeller mechanism have soaked in the heated hangar structure for a period of time sufficient to warm the elastomeric material of the seals, the variable pitch propeller mechanism can be manually manipulated without causing damage to the elastomeric material of the seals.
The procedure of heating an entire aircraft in order to facilitate the inspection of the variable pitch propeller mechanism requires that the aircraft be in a heated hangar structure for at least two hours. This procedure is expensive, because it requires a large volume of space to be heated in order to facilitate the inspection and maintenance of the variable pitch propeller mechanism, and it requires personnel and equipment to relocate the aircraft by towing it; it has the effect of limiting the capacity for inspection and maintenance in cold climates because the only variable pitch propeller mechanisms that can be inspected and/or maintained are those that have been in the hanger for a period of time; and it has an adverse impact on the ability to operate a fleet of turbo-prop aircraft into cold climates (or areas where a spell of cold weather is present, even if the climate is not cold) where hangar facilities may not exist.
The prior art relating to the heating of turbo-prop machinery, and particularly for heating the variable pitch propeller mechanism, does not address the specific matter of facilitating the maintenance of a hydraulic variable pitch propeller mechanism that is situated in a cold location.
U.S. Pat. No. 4,930,725 to Crag E. Thompson discloses a spinner configuration applied to a variable pitch propeller mechanism on a turbo-prop aircraft of the xe2x80x9cpusherxe2x80x9d variety. This is a configuration wherein the variable pitch propeller and variable pitch mechanism are located behind the turbine engine, and are subjected to the impingement of hot exhaust gases that result from the combustion within the turbine engine. One object of the ""725 patent is to keep the bases of the propeller blades from being affected by the flow of hot turbine exhaust; that is, the object is to keep the general vicinity of the propeller and variable pitch mechanism cool, rather than to promote the introduction of heat.
U.S. Pat. No. 4,393,650 to Francis C. Pool discloses a spinner configuration for covering the spinner of a turbine engine, where the turbine engine does not transmit its power to a propeller, but rather the direct thrust of the turbine engine is used to propel the aircraft. A portion of the spinner according to the ""650 patent is made of a flexible material for the purpose of impeding the formation of a thick ice layer on the spinner during flight operations.
U.S. Pat. No. 5,793,137 to James Andrew Timothy Smith discloses an electrical generator arrangement that may be applied to turbo-prop machinery. The electrical power produced by the generator according to the ""137 patent may be used to operate aircraft deicing facilities on the propeller(s) (column 2 line 50), the spinner that covers the variable pitch mechanism (column 2, line 50) or the leading edge of the aircraft wing (column 2, line 57).
The present invention is a method of warming a hydraulic variable pitch propeller mechanism using a flow of forced warm or hot air. This method may be practiced in the open, that is, it is not necessary to have the aircraft in a hangar structure in order to warm the variable pitch propeller mechanism.
The spinners on turbo-prop machinery that are equipped with hydraulic-actuated variable pitch propeller mechanisms typically have a hole in the front, for the purpose of admitting cooling air during the flight operation.
The method of the present invention may be practiced by forcing a volume of heated air into the volume defined by the spinner, using a structure that directs the flow of heated air into the hole in the front of the spinner. The source of forced heated air could be a ground-based heater unit having a flexible hose, and the structure for directing the flow of heated air could be a tube having an outside diameter that is slightly less than the inside diameter of the hole inside the spinner.
Using the method of the present invention, it is possible to warm a variable pitch propeller mechanism in about 10 minutes. This represents a significant saving of time over the previous method, which required first that the airplane be taken to a heated hanger, and second, a wait of at least two hours before the inspection and maintenance could commence (when the inspection requires the manual manipulation of the propeller pitch).
One object of the present invention is to provide a method of warming a cold variable pitch propeller mechanism for the purpose of inspection and maintenance without having to relocate an aircraft to a heated hangar structure.
Another object of the present invention is to reduce the length of time required to warm a cold variable pitch propeller mechanism for the purpose of inspection and maintenance.
It is another object of the present invention to warm a cold variable pitch propeller mechanism for the purpose of inspection and maintenance using facilities that are usually available at aircraft landing strips.
Another object of the present invention is to provide a method of warming a cold variable pitch propeller mechanism for the purpose of inspection and maintenance that may be practiced by a turbo-machinery mechanic or by other ground crew personnel.
The present invention relates to a method and apparatus for heating a variable pitch propeller mechanism that may be adapted and adjusted to accommodate any given propeller spinner configuration, and to accommodate any given source of forced hot or warm air. Specific features of the invention will be apparent from the above and from the following description of the illustrative embodiments when considered with the attached drawings and the appended claims.
In summary, and in accordance with the above discussion, the foregoing objectives are achieved in the following embodiments.
1. A method for heating a variable pitch propeller mechanism that is located in a cavity defined by a spinner, comprising the steps of:
a) taking a supply of warm forced air;
b) providing a facility to direct the supply of forced air into the cavity defined by the spinner; and
c) directing the supply of warm forced air into the cavity defined by the spinner.
2. A method for heating a variable pitch propeller mechanism as described in paragraph 1, wherein:
the front of the spinner has a hole;
the facility to direct the supply of forced air into the cavity defined by the spinner comprises a flexible hose; and further comprises a tubular construction where one end of the tubular construction fits into the hole in the front of the spinner and the other end of the tubular construction is fastened to an end of the flexible hose.
3. A method for heating a variable pitch propeller mechanism as described in paragraph 2, wherein the tubular construction has:
a smaller diameter front portion that fits into the hole in the front of the spinner;
a larger diameter flange portion that fits the flexible hose; and
a transition portion between the smaller diameter front portion and the larger diameter flange portion.
4. A method for heating a variable pitch propeller mechanism as described in paragraph 2, wherein:
the facility to direct the supply of forced air into the cavity defined by the spinner further comprises a screen.
5. A method for heating a variable pitch propeller mechanism as described in paragraph 1, wherein:
the front of the spinner has a hole;
the facility to direct the supply of forced air into the cavity defined by the spinner comprises a flexible hose; and further comprises a hollow structure where the interior surface of one end of the hollow structure conforms to the outside surface of the spinner, and the other end of the hollow structure is fastened to an end of the flexible hose.
6. A method for heating a variable pitch propeller mechanism as described in paragraph 5, wherein:
the facility to direct the supply of forced air further comprises a screen.
7. A method for heating a variable pitch propeller mechanism that is located in a cavity defined by a spinner, comprising the steps of:
a) providing a facility to create a supply of warm forced air;
b) providing a facility to direct the supply of warm forced air into the cavity defined by the spinner, where the facility to direct the supply of warm forced air is integral with the facility to create the supply of warm forced air; and
c) directing the supply of warm forced air into the cavity defined by the spinner.
8. A method for heating a variable pitch propeller mechanism as described in paragraph 7, wherein:
the facility to create a supply of warm forced air comprises an electrically-powered heating element and an electrically-powered blower.
9. A method for heating a variable pitch propeller mechanism as described in paragraph 7, wherein:
the facility to direct the supply of forced air into the cavity defined by the spinner comprises a tubular construction where the end of the tubular construction fits into the hole in the front of the spinner.
10. A method for heating a variable pitch propeller mechanism as described in paragraph 9, wherein:
the facility to direct the supply of forced air into the cavity defined by the spinner further comprises a screen.
11. A method for heating a variable pitch propeller mechanism as described in paragraph 7, wherein:
the facility to direct the supply of forced air into the cavity defined by the spinner comprises a hollow structure where one end of the hollow structure conforms to the outside of the spinner.
12. A method for heating a variable pitch propeller mechanism as described in paragraph 11, wherein:
the facility to direct the supply of forced air into the cavity defined by the spinner further comprises a screen.